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Young-Sun Paradox II

StarDate:

June 7, 2013

Most weight-loss plans start quick, then taper off a bit after you’ve lost a few pounds. And it’s possible that the same thing happened with the young Sun — it may have been a few percent heavier than it is today.

As a star ages, changes in its core cause it to get bigger and brighter. That means the newborn Sun should have been much fainter than it is today.

A fainter Sun would have been too feeble to warm Earth and Mars, leaving them as desolate iceballs. But there’s plenty of evidence that both worlds were warmer in the distant past than they are today.

One possible solution to that problem is that the Sun was a few percent more massive than it is now, which would have made it brighter.

Like all stars, the Sun blows some of its gas into space as a high-speed “wind.” Today, the solar wind is pretty thin. But young stars are much more dynamic than middle-aged stars like the present-day Sun. They spin faster, so they generate much more powerful magnetic fields, which drive much thicker winds. If that were the case with the Sun, then it could have simply blown away a few percent of its mass early on. And in fact, there’s evidence that the early solar wind was indeed much thicker than it is today.

The issue is by no means settled. But if the young Sun were a bit chunkier than it is today, it’s a good thing it slimmed down. Even a slightly heavier Sun would have been so bright that long ago it would have made Earth too hot for life.

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